Arc welding apparatus



March 19, 1957 H. J. BICHSEL ARC WELDING APPARATUS 6 Sheets-Sheet 1 Filed May 14, 1954 mmn w Enm bh .523 JOEPZOQ INVENTOR Harry J. Bichsel.

: ATTORNEY WITNESSES WW 7 March 19, 1957 H, J. BICHSEL ARC WELDING APPAR ATUS 6 Sheets-Sheet 2 Filed May 14, 1954 POWER SUPPLY UNIT March 19, 1957 H. J. BICHSEL.

ARC WELDING APPARATUS 6 Sheets-Sheet 5 Filed May 14, 1954 a .w u 4 p m A m w m m 3 m r C o 8 ll P m l m O M F m e o W r f S O l 0 w m m 8 4 0 So: 5a wuczom w om to Sam Fig. 9.

Straight Polarity Welding Current Amperes 2:52 :5 mmnuc ummam 9 2 March 1957 H. J. BI CHSEL ARC WELDING APPARATUS 6 Sheets-Sheet 6 Filed May 14, 1954 United States Patent My inventionrelates to are Welding apparatus .and has particular relation toapparatus-for--Welding inan inert n gas atmosphere.

In are welding in an inert gas atmosphere with a' con sumable electrode; it--has become the; practice to feed and consume the electrode at a high speed which is-of the order of several hundred inches per minute for an elec- 'trode of the order of A3 or A diameter. "The-elec trode is fed through a gun by a motor which rnaybe adjusted in speed independently eithe are voltage and requires no control responsive to the arc-voltage. "Because the electrode is fed at a high speed, 'electrole material becomes available at the-arc at a high rate, and any tendency of the are lengthto =vary maybe readily suppressed. lt-has then-become practicable temperate at lower open-circuit voltages than heretoforea nd in ac- -corda-nce with theteachings-of the priorart, low-open circuit voltage apparatus both of thegenerator'and reetifier type has been provided. Thegeneratorapparatus is cumbersome and costly. The rectifier:apparatus, -in

accordance with the teachings'of thepriorart-includes facilities for'varying the Welding current-which =is' in- Volvedandcostly.

lt is accordingly an i objects of my invention toflprovide -low'-voltage' arc-welding apparatus of 'the-rectifieretype of relatively simple and. low cost structure.

Anincidentalobject of my. inventionis toprovide a rectifier system having, facilities of simplerand':low=.cost structure for varying the output voltage.

l-he e'fiectiveness of the; operationof thelowppenicin -cuitvoltage welding apparatus just discussedrwouldrbe enhanced by-wthe facility ofthe apparatustoiadjust-itself electrically tovariations of the feed-speed of the electrode, that is, ofthe'rate of depositof electrode.-materialsothat the arc length remains constant. This is partic'ularlydesirable where'the operation-is to be;:.autmatic:. .or.semi

automatic. Now the arc voltage varies directlynviththe' arc length becoming; greater as :the arc. length. increases and smaller as the arc length decreases. 'Thisrnariation of are voltage itself-militates against-constant ;arc.:.length since in itself (Without any. change in current) ituWOLlld tend subjcct to radiation losses, to cause tlieflarcelength to increase further .once'it'starts to;increase,;-or.to-.decrease further once it starts'to decrease. 1-A,-c0mpensating change in current to counteract thisfeifect is; d sirable and; within reasonable limits, it. is --desirable:that--.;this.com-

; pensating s'effect belargep Thus,';.it is. .d.esirable; th t. (111' increase in arc. voltage .be accompanied; by; a largezidecrease in' welding current .and a decrease-in arc-voltage be accompanied by a'large increase in weldingcnrrent.

Amore specific object of my invention ;then: is. 10pm vide low voltage arc-welding. apparatushaving a 'charac :teristic'such'that a sm'allychange inv arc;voltage is accompanied by very large change in weldingcurr ,;;and 1 a large change in welding-current is accompan ed by a small, change. in arcivolt age.

;. In accordance with the specific, aspects ofmy inyentipn',"

I provide direct current arc-welding apparatus'whicli is 2,736,160 i cnta -Mar- 1 9, 1.9

2 .scnergized from apolyphase source rand the voltage of which is controlled by variable transformers capable of ;-:,in troduci ng voltage increments variable continuously from. a minimum to a maximum. This apparatus includes 5 a ;polyphase .transformerhavingsecondary phase, wind ings in series with each of which a secondary winding ofa-booster transformer is connected. Each ofv-these A nctworks. consisting of a. secondary .phase winding and a secondary booster winding in series isconnected to a loaterruina pfst t c e T p ima y. p a ind each supply a primary winding of a booster transformer through; a.- rev ersing switch and: one ofthe v variablei trans formers. The potential available at {thequtp t terminals of thev rect fi is depende .oa-t es m ra s mv o the -.the.re.c9. ary-w nd gs f h i pos ntran prmer. 4 71 secondary potential of each of the booster t-ransformers his: determin rine settin s-0 th assqei ted transf ormcr and; associated;reversing-switch. 20 :,reversing switch in one position gt e seeond ary potential ,.of;the booster-transformer isaddedto the econdary po- :tential. of l the associated csecondary phase- .w; ding; and with the reversing switch in the; opposite,pos ion,;the secondary ,potential of the.:b0oster .-trans fo rmer.; is sub tracted fromitheqassociated. secondarviphase pq finfial. Thus awide range ofvoltage variable insmallincrements is:available for welding. In addition,ithe voltage is -.variable continuously over; the. whole, rangetwithout -.,dis- 1 connecting the weldingzzelectrode and the.-work from :the 0:: supply;.;that is, theevoltage may lac-varied. over the .whole rarigeby-the operator while he;is welding Eorexample, starting. with the variable transformers. and switches'set cso' that. the voltage is a 'maximrimgthevariable transformers may be varied until their voltage is .zero; atwthis 35.:p'oint the switches maybe actuated without. aifectingithe ivdltagebetween the electrode andtheworkbecause the potential outputs of the variable transformers-are zero; ;thereafter the variable transformersmay beagain varied :until their voltages are amaxiniumand-the -voltage be- 40'tween the electrode and-the work is'aminimuni.

It isan important feature of a the power "supply; unit consisting of the supply transformer;the variabletrans- 'Qfor-mrsandbooster trans-formeiythatit is pf yery'low impedance, the ratioof open circuit-primarycurrent to --short circuit primary current beingp'referably' less-than I j i It is-because of this feature that the characteristic was described above, .such that a small change in arc voltage is accompanied by a-large changein elding current. o Specifically; for a low-voltage arc welder in accordance with'mydnvention', I provide a polyphase transformer, eachof--the secondary phasewindings of whiclris capable ofQdeliVering anopen-circuit voltage of theorder; of 21 I -vol ts'R'. M. S.- when energized from a,commercial supply of 220 or 440 volts, and a boostergtr'ans'fdr'mer variable i transformer combination which is'capable of delivering an open-circuit voltage from Zero to 10, volts 'R. M. S. across the secondaries of the booster transformer as the voltage across the primaries is varied from zero to 220 volts. Each of the networks, including a. secondary phase-winding and a secondary boosterwindinggis thus 'fcapable offdelivering betweenllvolts ant-1 31 volts R.- -M.' ssdepending on the setting of the associatedjvariabl'e transformer andreversin g switch. This voltage makes available at the output terminals of the re ctifier i an open-circuitvoltage range of between liand 40 volts. I--'thus provide an arc welderincludingfacilities for impressing a potential continuously variable of between '15 ,and '40 volts, between the el'ectrode and th, work. The novel features that I consider;characteristic ot at nyenti n a e tec .t en ra lrab --i hat-i tion itself'both as to'its organization and its method of operation together with additional objects and advantages thereof will be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Figure l is a circuit diagram of a preferred embodiment of my invention;

Fig. 2 is a circuit diagram of the embodiment shown in Fig. 1 which shows the relationship between the various windings of the transformer and the supply potentials impressed;

Fig. 3 is a fragmentary view showing the important features of the variable transformer used in the practice of my invention;

Fig. 4 is a circuit diagram showing a modification of my invention;

Fig. 5 is a graph showing volt-ampere characteristics of a tube embodiment of my invention shown in Fig. 1;

Figs. 6 and 7 are graphs showing the eificiency and the power factor respectively of the embodiment shown in Fig. 1 as a function of the current for the characteristics shown in Fig. 5;

Figs. 8 and 9 are graphs showing the burn off rate and the electrode feed speed respectively as a function of the current for the embodiment shown in Fig. 1;

Fig. 10 is a graph showing the relationship between the volt-ampere characteristic and the volt-ampere characteristics of the arc; and

Fig. 11 is a block diagram showing the important parts of the apparatus shown in Figs. 1 through 3.

The apparatus shown in Figs. 1 through 3 and 11 includes a Welder, a Power Supply Unit and a Control Unit. The main power supply for this apparatus are the power supply buses or conductors 11, 13 and 15 which may be connected to a three-phase supply of the commercial 60 cycle type. Usually, the power available at the conductors is at a voltage of 220 or 440, and the apparatus, in accordance with my invention, is adapted to operate at either of these voltages. In addition, power for certain control functions is derived from auxiliary buses or conductors 12 and 14 which are usually of the 110 volt 60 cycle type.

Since my invention is not in any way tied up with the mechanincal details of a welder, the Welder shown in Fig. 1 is of purely rudimentary structure. This Welder includes a gun 17 having a channel 19 through which a welding electrode 21 may be transmitted towards work 22 to be welded, a reel 23 from which the electrode 21 is derived and a drive 25 for the electrode 21. The channel 19 is provided with a brush 27 or other contact means for connecting the welding electrode 21 to the electrode conductor 29 of the power supply unit. The gun 17 also includes an inlet tube 31 through which inert gas is supplied to the channel 19. The channel 19 terminates in a nozzle 33 beyond which the melting tip of the electrode 21 extends during a welding operation, and at this time the inert gas supplied through the inlet 31 passes through the nozzle and envelops the welding electrode and the adjacent work 22 within an atmosphere within which the arc may be ignited and may operate at a low voltage. The gun 19 also includes a trigger 35 which may be actuated by the operator to close a switch 37 within the gun. The work 22 is conilIected to the work conductor 39 of the Power Supply Hit.

The drive 25 may be of any suitable type. It is shown symbolically as including a drive motor 43 and rolls 45 for advancing the electrode 21. The motor is supplied through a drive control 46 which is energized from the auxiliary conductors 12 and 14 through the trigger switch 37. The structure of the drive control 46 does not concern my invention and is not described in detail. Generally it includes facilities for starting and stopping the motor 43 and in addition for controlling its speed so that the rate of feed of the electrode 21 7 may be controlled.

The Power Supply Unit includes a rectifier 51, a

polyphase transformer 53, I former 55, a plurality of variable transformers 61, 63

from 220 volts or from 440 volts. It has a plurality of primary phase windings 53P1, 53P2, 53P3. Each primary phase winding has terminal taps 71 and 73 and an intermediate tap 75 which divides each phase winding into two sections 77 and 79. When the apparatus is en'ergized from a 440 volt supply, the sections 77 and 79 of each primary phase winding are connected in series andeach section 77 and 79 may be regarded as the secondary of an auto-transformer from which 220 volts may be When the derived with 440 volts across the primary. apparatus is energized from a 220 volt supply, the sections 77 and 79 are connected in parallel. The polyphase transformer 53 also has a plurality of secondary windings 5381, 5352 and 5353. The polyphase transformer 53 is of low impedance. The booster transformer 55 is of low impedance and has primary windings 55P1, 55P2, 55P3 and secondary windings 5551, 5582, 5553.

Each of the variable transformers 61, 63, 65 is of the type sold in the trade under the names of Variac or Powerstat variable transformer. This variable transformer is of low impedance and its important features in addition to the low impedance, as far as my invention is concerned are shown in Fig. 3. As shown, the variable transformer is composed of a large number of closely spaced but insulated turns 81 wound on a toroidal core 83. Each of the turns 81 is of circular form with the portions of the turns 85 on the upper face of the toroidal core 83 flattened and free of insulation, and a conductive slider 91 which is connected to an axial shaft 93 and is movable by rotation of the shaft engages the insulationfree turns 85. The variable transformer has a pair of end terminals 97 and 99 between which all of the turns 81 are preferably included. As the slider 91 is moved from one end terminal, say 97, to the other, 99, it changes the number of turns 81 between it and both of the terminals. Because the turns 81 are closely spaced and because the slider 91 engages a number of the turns, the number of turns between the slider and each of the terminals 97 and 99 is variable, not in steps, but for all practical purposes continuously, from a low magnitude to a high magnitude with reference to one of the terminals, and from a high magnitude to a low magnitude with reference to the other terminal. Thus, the ratio of the number of turns between the fixed terminals 97 and 99 of the variable transformer and the turns between the slider 91 and either of the terminals is continuously variable, and the voltage available from the variable transformer is continuously variable. The slider 91 of the variable transformers 61, 63, 65 are ganged so that the variable transformers may be set as a unit.

While the component (61, 63, 65) just described, which is preferred in accordance with the specific aspects of my invention, is designated in the art as a variable transformer, it may be regarded as a variable inductive reactance or a variable impedance somewhat similar to a voltage divider. In referring to a variable transformer herein and in the claims, I intend to include within the broad scope of my invention the component of the type disclosed or a similar low impedance component for per forming the same function as the variable transformer, that is, for supplying to the booster transformer a voltage capable of continuous, as distinct from step adjust ment, regardless of what such component may be called or of the specific character of its structure.

Each of the reversing switches may be of any wellknown type and is shown symbolically as in the form. of a drum having a plurality of fixed contacts 101., 103. and 107 and cooperative sets of movable contacts 111 and 113 and 115 and 117. Each switch has two a polyphase booster transtaps 105 and 1111 respectively. switches are imposition I, the left-hand terminals 97 of the variable transformers are connected to the..terminal .taps' 71 of thesecondary phase windings andv therighthand terminals 99, of the variable transformersare con- I primary phase winding.

positions,- a: first position I inzwhich themovable contacts I @Therectifier 51- consistsof a plurality of pairs of units ';;51R1, 51112;;51113, 51R4,---51R5, 51-116; each pair being associated with- -a-- phase: of -the transformer. .The anode --:of.-one rectifier 51R2,-.51R4;- 51R6 of eachpaira. and" the cathode ofstheother '1R1',-. 531R3, -51R5are connected together to form junctions 131, 133.:and 135 respective- 1y. -.The cathodestof the former rectifiers 51R2, 51kt, l 51-R6 of three pairs areconnected to-conductor-29- and .-theanodes of the latter reotifiers. -51R1,.-51 R3, SIRS of 1 -.the three 'pairs are connected. to conductor 39.

slur-the preferred practice of \my invention, the second- ;ary. phase windings 5381, 53S2,.53S-3..ofthe transformer 53 are-connected each in series withan.associatedcbooster secondarywinding5581, 5582, 55'S3,.--and.-cach of these latter .series networks are .connectedin series into a polygonal or .delta'network. The -apices-141; .-143 and l45of.the deltaare.connectedzrespeotively to the'juncdons-131, 133 and 135. When: the transformers 53 and .55. are-energized, positivescurrentmay thus :be. conducted :to conductor 29 from apices 141 1 -43, 145. and fromcon- .ductor 39 tothe apices. By positivecurrent, I-mean the .fiowof-positiveions. or -holes, as they .arecalled in the ;art,.as vdistinct from electrons. While-in-the apparatus -.shown in Figs. 1- ,and. 2; theelectrode conductor- 29 is thus of positivepolarity-relativetoathe' work. conductor .39, in the practice of my invention,: the connectionsmay ibereversed and frequently are so that the welding-electrode is electrically. negative and theworkpositive.

In the preferredpractice of my-invention the primary ,LPhase windings :53P1, 53P2 andl52P3 areconnectedin a polygonal or deltaconfiguration having .apices:151, 153

.and. 155. Input supply conductors.161=-, .163 and 165 are :lconnected respectively tothe apicesi 151, .153, 155.

vThe terminal :connections 97 and99- of .each of the variable transformers. 61,.63, .65 arevconnected through the associated reversing switch 67, 69and 70 respectively across a section 77.ofthe associated primary phase winding 53P1, 531 2, 531 3 respectively. .Forthis purpose, the terminal connections 97 .and 99...of each :variable transformer are, connected respectivelyto fixed contacts 103 and 197 of the associated reversing. switch, and the intermediatetap75 .and one of the terminal. taps 71 of. the associated phasewinding areconnectedto fixed Whenthe reversing nected to the intermediate taps 75 of the phase windings; when the switchesare in position .ILthe left-hand terminals 99 of the variabletransformers are connected -to the intermediate tap 75 of the primary phasewindings and the right-handterminals97'of the variableitrans formers are connectedtothe terminal =-taps 71 of. the The vadjustable slider 11 of each. of the variable transformers 61, 63, 65 and one of .the terminal taps 99 are connected respectively across associated. primaries 55131, 5512, 551 3 respectively of the booster transformer 55.

In the preferred practiceof my invention, thewindings ofthe polyphase' transformer 53 are-so related that of the order of21volts R. M. S. appears acrosseach of the secondary phase windings 5381, 5382, .5383 when 220 or v 440-. volts is impressed across. the primary phase :windings f',53P1';'. 531 2, 'J-S3P3 properly .connected, and the windings of the booster transformer 55 are so related that when the associated variable transformer.i 61,..63, 65 is inithe position todeliver thetmaximum voltage, thatis 220 volts R. M. S., the potentialuwhich :appearsacrosseach secondary isr'of theorder of. volts R. M. 8. .Thus, the

R. M. S. potential across each of the networksconsisting of a secondary phase winding 5381, S2; 83. and the associated secondary winding 5581, -5582,..55S3..:of...the booster. transformerrmay, depending. onthe position of theassociated-reversingswitch 67,69, 70 be either 11 or 31 with each variable'transformerin.the-position-to deliver-the maximum voltage. Thisvoltage may, be,.varied substantially continuously from 11 volts. to 31-.,volts or in the opposite sense as the setting ofrthe associated..variable transformer is: changed. The. corresponding direct cur- 15f rent voltages which. are impressed between 7 the. electrode conductor .andwthe work.conductonvaryrfrom-15..volts to 40 volts. This .voltage. is adequate. toiire and .maintain are between an; electrode and. work :in. .an inerL-gas atmosphere'when the electrode.material=- is supplied at 21 8116611 of several inches per .minute.

{lThe.-Contro1. Unit. includes a pluralityof normally open contacts 171, 173 and 175 .actuable sby -.a..so1enoid 179. The contacts 171, 173, 177, -.when-c1osed, connect 1 the inputsconductors161,.163, 165 of. the Powe'rSupply 25 -.The--Ccntrol Unit.:also-includes arelay .181. having a Unit to the power-supply buses 11, 13,.and'15 respectively.

:- norrnallynopen.contact.183. IThe normally open contact -.-.183. is .connectedin series with .the .s0lenoid179 .across supply conductorslland 13.- .Thecoilof the relay .181

isactuated by theclosingof a contact 184 in, -the.drive control 46 when thelatter is. energized. TheQControl Unit further includes an ,iautotransfor me'r. 195 energized -from the two-conductors 11 and13 -which Supplies a motor 117. for. actuating acoolingfan199.

formed by. a 3%" stack of Westinghouse Style. Nos.

1458861 and 145 8166 punchings interleaved, on each leg of which a primary phase Winding coil (53191,...53P2, 531 3 )v and a secondary phase winding coil (5381, 5352,

. 5383) are mounted. .The primarycoils are nexttothe associated legs and vthe secondary coilsencircle the associated primary coils. Each primary phase windingcoil .has 250 turns of .081" diameter. copper, wire of circular section, is 6 /2 in diameter and 4 /8 long. Each secondary phase Winding coil has 12 turnsproduced bywinding four parallel copperconductors of .114" by .182 dimensions, is 7%" in diameter and is 4% long. The impedance of the transformer 53. defined astheiratio of the primary current with the secondary at open circuit to the primary current with the secondary at short circuit multiplied by 100, is 6.1%.

Transformer 55-Consists of a three-legged core formed by a 2 /8" stack of Westinghouse punchings Style Nos. 1499283 and 1499284 interleaved, on each leg of which a primary winding coil (55P1, '55P2, 55P3) and a secondary winding coil (55S1, 5582, 5553) are mounted. The primary coils are next to the associated core-legs and the secondaries encircle the associated primaries.

Each primary coil has 176 turns of .064" diameter copper Wire of circular section, is4 /s" in diameter and 3% long. Each secondary coil has 8 turns produced by winding four parallel copper conductors of rectangular section of .114" by .182" dimensions; is 6" in diameter and 4 long. The impedance of this transformer 55 is about 5%.

Variable transformers 61, 63, 65Each is-catalogue No. 1226-12313 Powerstat transformer madejbySuperior Electronic Co. of 3 Clarke Avenue, BristoLConnecticut.

'3 transfer switch, style B, form 6PDT, 2 position, Bulletin 806, rated 10 amperes and 280 volts.

Contactors 171, 173, 175Westinghouse NS contactor size 2 Style No. 1577306.

Relay 181Potter-Brumfield MRlA with 115 volt 6O cycle coil.

In the standby condition of the apparatus, the switches or circuit breakers (not shown) to the supply conductors 11, 13 and 15 are closed and the supply conductors are energized. The fan motor 197 is thus energized actuating the cooling fan 199. In addition, power is available between the conductors 11 and 13 across which the solenoid 179 is adapted to be connected and also between the conductors 12 and 14.

When a weld is to be made with the apparatus, the electrode 21 is passed through the gun 17 so that its end projects through the nozzle 33. The gun 17 is then held in the hand and the trigger compressed. A circuit is thus closed through the coil of the relay 181 actuating the relay. The normally open contact 183 of the relay closes the circuit through the solenoid 179 actuating the contacts 171, 173, 175 so that power is impressed at the terminals of the delta network of the primary phase windings S3P1, 53P2, 53P3.

Power is now available between the welding electrode 21 which is connected to the electrode conductor 29 and the work 22. In addition at this time the gas valve (not shown) is opened and gas flows to blanket the electrode and work in an atmosphere of inert gas. The operator now touches the electrode to the work and the electrode vaporizes and an arc is struck between the electrode and the work, the drive motor for the electrode 21 is actuated and the welding may proceed.

The manner in which the apparatus in accordance with my invention operates is illustrated by the graphs presented in Figs. 5 through 10. The data on which these graphs are based was derived from measurements taken while producing sound welds with ordinary hot rolled steel work and a ferrous electrode having a diameter of A coated with an arc stabilizing oxygen containing material, the electrode being of the type disclosed in a copending application Serial No. 432,958, filed May 28, 1954, to Julius Heuschkel and Howard C. Ludwig and assigned to Westinghouse Electric Corporation.

Fig. 5 presents the voltage-current characteristic of my apparatus at three different settings of the variable transformers 61, 63, and reversing switches 67, 69, '70. Voltage is plotted vertically and current horizontally. Curve A corresponds to a setting for an open circuit voltage of 40 between the electrode conductor 29 and the work conductor 39, curve B to a setting for an open circuit voltage of 27.5 volts, and curve C to an open circuit voltage of 15 volts. In deriving the data for curves A, B, and C the apparatus was set at each of the respective opencircuit voltages and the voltage and current measured for different resistance between the electrode conductor 2'9 and the work conductor 39. It is seen that at each setting the change in current for a change in voltage is large. Thus in the neighborhood of 500 amperes at which the apparatus is designed to operate continuously a change of amperes corresponds to a change of only one volt. It is seen that under such circumstances the facility for setting the voltage continuously over the range is desirable.

Fig. 6 presents the efiiciency of my apparatus as a function of current for the situations represented by the graphs A, B and C of Fig. 5. Efficiency in percent is plotted vertically and current horizontally. The graphs of Fig. 6 are labeled to correspond to Fig. 5. It is seen that the etficiency increases materially with the open circuit voltage.

Fig. 7 presents the power factor of my apparatus as a function of current for the three situations in Fig. 5. In this case power factor in percent is plotted vertically 5 and current horizontally. The power factor seems to be a maximum for the intermediate open circuit voltage.

Figs. 8 and 9 show how the burn-off or melting rate of the electrode in the practice of my invention and the feed speed of the electrode vary with welding current. In Fig. 8 burn-cit rate in pounds per hour is plotted vertically and current horizontally and in Fig. 9 electrode speed in inches for a minute is plotted vertically and current horizontally. It is seen that as the burn-oft rate or feed speed increase the welding current also increases. Thus with the burned rate at 300 inches per minute the welding current is about 480 amperes and with the rate 400 inches per minute the current is 570 amperes. It appears then that as the setting of the control 46 is changed for different electrode feed speeds the welding current is changed materially.

Now there is a relationship between welding current or arc current and are voltage which must be maintained to maintain normal welding. If for any open-circuit voltage setting of the apparatus the current becomes so small as to fail to satisfy the relationship the arc is interrupted and if the current becomes so high as to fail to satisfy the relationship stubbing takes place. Stubbing is defined as the condition in welding when the electrode is near the work and the current is just too low so that the electrode touches the work intermittently.

The relationship between arc current and are voltage which must be maintained and the manner in which it is maintained may be understood by comparing the arc voltage-current characteristic for given are lengths with the apparatus voltage-current characteristic and a comparison as presented in Fig. 10. In this case the voltage between electrode conductor 29 and the work conductor 39 is plotted vertically and current horizontally. The apparatus characteristic is represented by the curves A, B, C, which are the same as the similarly labeled curves of Fig. 5. Two arc characteristic curves are presented, the upper, labeled N, corresponding to normal welding; the lower labeled S corresponding to the limiting condition in which stubbing occurs. The data for curves N and S was derived by setting the apparatus at different open circuit voltages and at each voltage first welding normally at a given arc length and measuring the current and then decreasing the arc length until stubbing occurred and measuring properties and at least in part on the properties of the material being welded. In the case at hand the curves N and S are for the coated ferrous electrode described above.

The curves A, B, C and N, S are representative of families of curves corresponding to different settings of the variable transformers and electrode feed speed. Each welding operation is represented by curve such as B and a curve such as NA and the point of operation is of their intersection. During any Welding operation the settings must be so coordinated that in spite of the usual fluctuation of the welding current and supply voltage the welding proceeds without stubbing or without arc outages. For any set of curves N and S then the open circuit voltage must be so selected that the corresponding apparatus characteristic curve intersects curve N in the region of a current magnitude at which the apparatus is designed to operate. Thus for the curves N and S, the open circuit voltage should be such as to correspond to a family of curves in the region of curve B; if it corresponds to curves A or C the apparatus will fail to weld properly.

For a better understanding of the operation assume that the variable transformers and the electrode feed speed are set to correspond to the curves B and N. The voltage and current in the region of which the operation takes place is at this setting given by the intersection of these curves; that is, the voltage is 23.5 and the current 324 amperes. The corresponding feed speed (Fig. 9) is inches per minute. Now assume that the feed speed is increased to 250 inches per minute. This results in an increase in current 414 amperes. By increasing the electrode feed speed the arc length has been decreased.

i fhe operationis thenalonganother curve of the family N .-:which has a point havingan abscissa 'of 414" amperes. 1'. It is seen that this point -lies on curve Bat an: ordinate niof abouti 2'2.8 volts. 'The new N curve N' must psss 1- through this p0int. Thus a curve-of the: family, N, tapproximately: =pa'ralleh to N and S is defined. Since this curve is above S' the welding at: the newspeedwill probably proceedvnormallygi=l3ut=toaassure stability it may be e desirable to raise the open circuit voltage" slightly thus raisco ing the 1B curvesothat approximately the original N curve definesthe operation. Anew curve B is. thus obtained. 5 Itisseenatha'ta to, achieveithe desired-coutrolof feed zzspeed andzarc voltage .the flexi bilityof control aiforded by the apparatus in accordance with my invention is essential. wsTheavari-able@transformers.61,1 63,65 afford facilities to enable :the operator-to adjust preciselytheopen circuit oltageuavailablerbetween the electrode and the work, 1n; nd thus. ton'coordin-atethe arc voltagewith'thecurrent at which 'thenweldingtakes place which is inzturnde- -;=:pendent':-.in.= the rate at which the electrode is supplied.

itwT-The @bo'oster'.transformer 55 is wound to reduce a po- 2 tentialfofj'220cvolts to approximately .10. MORS. ;1The:rela- .ittionshipabetween the;secondary: 55S1, ::5'5S2;1r5583 .and the primary 55P1, 55P2, 55P3..ofwthenwindings ofthe eboostentransfouner isthus, in eifecaethatwhich exists :obetween a conductor. and the windings. of a current-transstwformer coupled; to the .conductor. .This relationship is :ofgparticular:importance when the variablextransformers 61,263, 651 are set in the position in which: the potential ecdcliveredzby: them iszero. lnlthiscase, a highpotential LIL can {be rinduced from. a secondary iwinding of. the. booster 1 iransformer into a primaryxwinding iwhen weldingcur- -x'zrentor zshort circuitcurrent flows through the:;primary ;-,:network:'on the; primary \circuit isopen. Under vthei ciroumstances; it; is :aessentiadrtlilaty. the :slidersr91 vzbecconiESiIU cted sufiicientlymassive to conduct the .cun'ent-qwhich i1 .thu's fiows.

t 1 Within} the broad aspects of. my :invention,; .the:'revers- ;-i;:1ng-,= switches 67,169,: 2742' could in; each case be. connected .-,-=between a variable transformer 61,.63,:65;.andt.the-pri- -mary;SS,P.l, SSPZ', .55P31-0f the.booster.transformenrather *zthanvbetween. each of the: primaryxphase windings. and a r,=variable-:transformer, but;.r-such-. a connection is: not; to .-:be preferred. vWith. the switch connected-between: the ,zvariableztransformers and theprimaries of; the flbOQStfiI' 1 :.Ira115f01m6r,thecontacts of: the \SWiiCimS'zWOl ld be subsq'ected tozhigh potentialby actuation;when:;current is :flowing in:;the welding circuit-by reason of the, current transformer effect just described. Suchyhighx potential would: cause arcing. at the contacts, would seriously :dam- 50 r-mageathe switcheand may also causeshorteeircuitingtof the .zpowerr supply.

ml iiththe switches 57,769,?70 connected asEShOWnin -Fig. l the welding voltage may. be-varied under loadifrom the minimum magnitude to the .-maximum: magnitude,

without damage to the switches or toany-othcpparts, by tqmoving the tapsz9-ll ofthewariable transformersfil, 63, '65 :from maximum. to; zero output ,vzand :reversing- ;the --.:switches at zero output. Thus, an operatorsmaysetthe voltage at precisely'the proper magnitude as he is;we ld -ing;

:he need not guess at the setting and then weld to deter :mine if hissguess is correct.

The-apparatusshown in Fig.- 4 differs-from the; ap- 'aparatusshowninFigs. lithrough 3 onlyin-the factz'that 1 it; :includes .yariable transformers {201, 2ii3,- 2e 5, .ofqthe type having a fixed intermediateconnection207 inaddition to theadjustableslider2ti9 Suchvariation trans- *formers-permitthe elimination of the reversible switches --.67; 6 9 and Hot Fig. 1.

; Incthe Fig. 4,-moditication, the terminal connections lllrand 213 of the variable transformers are'each connectedbetween an intermediate tap"75;and a terminaltap 5:15-01? asection 7.7 of a-corresponding primary phase-winding:53P1-,:53P2, 5:3P3and each of;theassociated-primaries 55P1, 55P2, 55P3 of the booster transformer is connected i ii? zobetween ztheradjustable gslider 208 and; the. intermediate ;::connection-i207.' The .zpotential" existing across :each-sr of the secondariesa55S1, 5552;".5583 of: theboostertransformer issdependent inmagnitnde on thennmberiofturns 5 x between .the' sliden'2il9 and the intermediate :termina11207 xzand inrpolarityron the position ofthe sliderrelative toithe hcintermediatezzterminal. Thus, the potential. @ayailable :;;across each :seriesmnetwork;"consisting of a ;.secondary phase -windingr-53S1; .-531S2, :5583 and a; secondary; 55.81,

1 5582, 5553 of. the:associated;booster transformer isivari- .ableovcr-a rangeqsirnilar-to therange afforded bythe Fig. napparatus. Itis essential in-the. casegoffig. 4 also that-ether voltage impressed through the-r :variable: ttransformerslfll, 203,205 shall be continuouslyevariablefrom a low magnitude to a highmagnitude.

While lhaveshown anddescribed certain specificembodiments of my invention, many modificationsthereof ware-possible. -.l\ iy-invention,-. therefore,- is. not to be -.;.-restricted except .insofarasis necessitated by, the; prior 293G11- .Lclaim as my invention:

l.-,- Appa1 atus"-for-welding with an arc between -an welectrode andiwork including incombinatiou ail-electrode conductor, a work conductor, a polyphase transformer d1aving aeprimarynphase winding and a-corresponding secondary phasewinding for each of'its phases, a variable -.transformer,. ;the turn ratio of which is capable. of con- .atinuousvar i'ation from amaximum magnitude to a minigemurn mag-nitude,=.associated with each phase of said ;-source-,eachsaid-variable transformer having fixed, terrrninalsiand anadjusting'slider movable between said'fixed wterminals, a reversing switch means associated withv each .5.-.phase of: said source and. having an actuating mechanism, asbooster transformer. primary winding and abooster 35. transformer secondary" winding :associated with each phase. of said -source,*means connecting in a series loop eat-least a portionof each said primary. phase winding, --the associated reversing switchand the fixed terminals of the associated variable transformer, means connecting 40 in aseries loop a booster-primary winding and the adjustableslider-and one of-the fixed terminals of the. as- AI.sociatedvariabletransformer, means connecting in. series ,-.in a- .deltainetwork -the secondary phase windings and -the secondary booster transformer windings, means-mechanicallv-couplingsaid adjustable sliders to move to- ,gether,-means mechanically=coupling the arms ofsaid 'reversingswitches to move together, rectifier'means, and means connectingsaid'rectiiier means between said-elec- .trodeand work conductorsso-that said rectifier means is capableofadelivering direct current through said;con-

, 1 du'ctors.

. 2'.--Apparatus for welding with an are between anelectrode. and worlcincludingin combination an electrode conductor-,awork conductor, a polyph'ase supply transformer having aprimary phase winding and asecondary phase-.winding'for each of its phases, a'booster transformeriprimary winding and a booster transformer secondary windingsassociated with" each phase of said supply transformer, means connecting in series in a polygonal network 0 said. secondary phase windings and the booster secondary windings, arectifier means, and means connecting said rectifier means between-said network and said electrode and W0rk;-.conductors,,the said apparatus being characterized by a variable transformer associated with each phase. of said supply transformer, eachsaid variable transformer having input terminals and outputterminals .and-the number ofits turns between the output terminals .beingvvariable continuously from a maximum magnitude to a ,--mi-nimum magnitude, said apparatus being also characterized by areversing switch means associated'with :each phase of said supply transformer, by means connecting the input terminals of eachsaid variable transformer to itsrassociated primary phase winding,-throughpthe -associated switch means, by means connecting the output terminals of each variable transformer across the associated booster primary winding, by means for setting all said variable transformers together and by means for actuating all said switch means together.

3. Apparatus according to claim 2 characterized by a plurality of phase conductors for supplying power from a polyphase source, by contactor means for connecting said phase conductors to the primary phase windings and by means connected to be energized from a pair of said phase conductors for actuating said contactor means.

4. Apparatus according to claim 2 characterized by means connecting the primary phase windings in a polygonal network, by a plurality of phase conductors for deriving power from a polyphase source, by a contactor means interposed between each phase conductor and a corresponding apex of said network, and by means connected to be energized from a pair of said phase condoctors for actuating said contactor means.

5. In combination a polyphase supply transformer having a primary phase winding and a secondary phase winding for each of its phases, a booster transformer primary winding and a booster transformer secondaiy winding associated with each phase of said supply transformer, a variable transformer capable of continuous variation from a maximum magnitude to a minimum magnitude associated with each phase of said transformer, each said variable transformer having first terminals between which the number of turns remains fixed and second terminals between which the number of turns is variable, a reversing switch means associated with each phase of said supply transformer, means connecting said secondary phase windings and said booster secondary windings in series in a polygonal network, means connecting each of said primary phase windings to one said set of terminals of the associated variable transformer through the associated reversing switch means, means connecting the other said set of terminals of each said variable transformer across the associated booster primary winding, rectifier means, and means connecting the apices of said network to said rectifier means.

6. Apparatus for welding with an are between an electrode and work including in combination an electrode conductor, a work conductor, a polyphase supply transformer having a primary phase winding and a secondary phase winding for each of its phases, a booster transformer primary winding and a booster transformer secondary winding associated with each phase of said supply transformer, means connecting each secondary phase winding and the associated booster secondary winding in a series network, a rectifier means, and means con necting said rectifier means between said series networks and said electrode and work conductors, the said apparatus being characterized by a variable transformer associated with each phase of said supply transformer,

each said variable transformer having input terminals and output terminals and the number of its turns between the output terminals being variable continuously from a maximum magnitude to a minimum magnitude, by a reversing switch means associated with each phase of said supply transformer, by means connecting the input terminals of each said variable transformer to its associated primary phase winding through the associated switch means, by means connecting the output terminals of each variable transformer across the associated booster primary winding, by means for setting all said variable transformers together and by means for actuating all said switch means together.

7. in combination a polyphase supply transformer having a primary phase winding and a secondary phase winding for each of its phases, a booster transformer primary winding and a booster transformer secondary winding associated with each phase of said supply transformer, a variable transformer capable of continuous variation from a maximum magnitude to a minimum magnitude associated with each phase of said transformer, each said variable transformer having first terminals between which the number of turns remains fixed and second terminals between which the number of turns is variable, a reversing switch means associated with each phase of said transformer, means connecting each secondary phase winding and the associated booster secondary in a series network, means connecting each of said primary phase windings to one set of terminals of the associated variable transformer through the associated reversing switch means, means connecting the other set of terminals of each said variable transformer across the associated booster primary winding, rectifier means, and means connecting said series networks to said rectifier means.

8. Apparatus according to claim 2 for welding in an inert gas atmosphere characterized by the fact that the polyphase transformer, the booster transformer windings and the variable reactor are so wound that, the direct current potential impressed between the electrode and work conductors when the apparatus is energized lies between approximately 15 volts and approximately 40 volts.

9. Apparatus according to claim 8 characterized by a polyphase transformer and booster transformer windings of low impedance.

10. Apparatus for welding by means of an are between an electrode and work including in combination an electrode conductor, a work conductor, a polyphase supply transformer having a primary phase winding and a secondary phase winding for each of its phases, a booster transformer primary winding and a booster transformer secondary winding associated with each phase of said supply transformer, means connecting in series in a polygonal network said secondary phase windings and the booster secondary windings, a rectifier means, and

means connecting said rectifier means between said network and said electrode and work conductors, the said apparatus being characterized by a variable transformer associated with each phase of said supply transformer, each said variable transformer having input terminals and output terminals and the number of its turns between the output terminals being variable continuously from a maximum magnitude to a minimum magnitude, said apparatus being also characterized by means connecting the input terminals of each said variable transformer to its associated primary phase winding, by means connecting the output terminals of each variable transformer across the associated booster primary winding, and by means for setting all said variable transformers together.

11. Apparatus according to claim 10 characterized by variable transformers each having a pair of end connections, an intermediate connection and an adjustable connection, the input terminals of said variable transformer being the end connections and the output terminals being the intermediate connection and the adjustable connection.

12. Apparatus for welding with an are between parts to be welded including conductors for supplying welding current to the parts, low impedance power conversion means having input terminals adapted to be connected to power supply conductors and output terminals, said conversion apparatus including continuously-variable, variable transformer means connected between said input terminals and said output terminals for varying the potential at said output terminals with a given potential between said input terminals, and means connecting said output terminals to said welding current supply conductors, the said apparatus being characterized by the fact that the variable transformer means is so connected between said input terminals and said output terminals that the potential at said output terminals is variable continuously over the whole range of said variable trans former means whereby the variation over the whole range may be effected under load, the connection of the variable transformer between the input and the output terminals being such that the potential of said variable transformer may be impressed between said output terminals selectively either as a bucking or a boosting potential component.

13. Apparatus for welding with an are between parts to be welded from a direct current supply having an open circuit voltage of between about 15 and about 40 comprising in combination conductors to be connected to said parts for conducting welding current to said parts, a polyphase transformer having windings each having connections between which a voltage of 220 R. M. S. is derivable, a plurality of variable transformers corresponding in number to the phases of said polyphase transformer and each having input and output terminals,

means connecting said input terminals of each variable transformer to said connections of a corresponding primary winding, booster transformer primary winding means corresponding in number to the phases of said polyphase transformer, a booster-transformer secondary winding means coupled to each of said booster transformer primary winding means, rectifier means, means connecting each said booster transformer primary winding means to the output terminals of a corresponding variable transformer, and means connecting said booster transformer secondary winding means in circuit with said windings of said polyphase transformer, said rectifier and said conductors so as to deliver a direct current voltage variable continuously from 15 to 40 between said conductors.

14. Arc welding apparatus according to claim 10 characterized by a polyphase supply transformer across each secondary of which a potential of the'order of 21 volts R. M. S. appears when a potential of the order of 220 volts R. M. S. is impressed across each primary and by variable-transformer booster-transformer combinations such that when the variable transformer is set for its maximum output the potential of the secondary of each booster transformer is of the order of 10 volts R. M. S.

15. Apparatus for welding by means of an are between an electrode and work including in combination an electrode conductor, a work conductor, a polyphase supply transformer having a primary phase winding and a secondary phase winding for each of its phases, a booster transformer primary winding and a booster transformer secondary winding associated with each phase of said supply transformer, means connecting in series in a polygonal network said secondary phase windings and the booster secondary windings, a rectifier means, and means connecting said rectifier means between said network and said electrode and Work conductors, the said apparatus being characterized by a variable transformerassociated with each phase of said supply transformer, each said variable transformer having input terminals and output terminals and means for varying the potential between said output terminals for a given potential between said 'nput terminals continuously from a maximum magnitude to a minimum magnitude, said apparatus being also characterized by means connecting the input terminals of each said variable transformers to its associated primary phase winding, by means connecting the output terminals of each variable transformer across the associated booster primary winding, and by means for setting all said variable transformers together.

16. Apparatus for welding with an are between parts to be welded including conductors for supplying welding current to the parts, low impedance power conversion means having input terminals adapted to be connected to power supply conductors and output terminals, and low impedance rectifier means to which said output terminals are connected to derive direct current, said conversion apparatus also including continuously-variable, variable transformer means connected between said input terminals and said rectifier means for varying the potential at said output terminals with a given potential between said input terminals, and means connecting said output terminals to said welding current supply conductors, the said apparatus being characterized by the fact that the variable transformer means is so connected between said input terminals and said output terminals that the potential at said output terminals is variable continuously over the whole range of said variable transformer means whereby the variation over the whole range may be effected under load, the connection of the variable transformer between the input and the output terminals being such that the potential of said variable transformer may be impressed between said output terminals selectively either as a bucking or a boosting potential component.

References Cited in the file of this patent UNITED STATES PATENTS 1,453,491 Champlin May 1, 1923 1,620,619 Currier Mar. 8, 1927 2,567,476 Hamilton Sept. 11, 1951 2,644,109 Mulden June 30, 1953 FOREIGN PATENTS 484,683 Germany Oct. 26, 1929 858,279 Germany Dec. 4, 1952 881,091 Germany June 25, 1953 896,099 Germany Nov. 9, 1953 857,947 France Apr. 29, 1940 

